Redmine

Workflow permission of "read-only" on a Custom field with "required" checked will prevent submission of issues.

Validation of required fields for which users have "read-only" permissions should be skipped when creating or updating issues; or an option should be created to allow a required field to be skipped if "read-only" when setting a field to required.

Steps to reproduce.
1.) Create a custom Issues field (ex. Billable w/ Format = list)
2.) Make sure to make this field required.
3.) Under Workflow -> Fields permissions set this new custom field to read-only for any role or tracker (ex. Role: Client & Tracker: Feature)
4.) Login as a user with a role with read-only permission on the custom field. (ex. Client)
5.) Attempt to create a new Issue or Update an issue with the custom field unset.
6.) On saving the user will be told that the custom field is required, but they are unable to view or change this field.